What laboratory tests should be ordered to evaluate low energy availability in an athlete?

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Last updated: March 29, 2026 • View editorial policy

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Laboratory Tests to Evaluate Low Energy Availability in Athletes

When evaluating an athlete for low energy availability (LEA), prioritize measuring reproductive hormones (estradiol, LH, FSH, testosterone), thyroid function (T3, TSH), metabolic markers (leptin, IGF-1), and bone turnover markers (βCTX-1, P1NP), along with vitamin D, iron studies, and complete blood count. 1, 2

Core Hormonal and Metabolic Panel

The most critical laboratory tests target the endocrine disruptions that occur with problematic LEA:

Reproductive Hormones (Essential)

  • Females: Luteinizing hormone (LH), follicle-stimulating hormone (FSH), estradiol, prolactin, and pregnancy test 1
  • Males: Testosterone (total), LH, FSH 1, 3
  • Rationale: Menstrual dysfunction in females and low testosterone in males are among the most sensitive markers of chronic LEA. Athletes with amenorrhea or testosterone in the lowest quartile show 4.5-fold higher bone injury rates 4

Thyroid Function

  • Triiodothyronine (T3), thyroid-stimulating hormone (TSH), T4 1
  • Rationale: Low T3 is a consistent marker of chronic energy deficiency and reduced resting metabolic rate. Studies show T3 decreases significantly in athletes with LEA, while it often remains stable in short-term experimental LEA 5, 6, 4

Metabolic Markers

  • Leptin: Consistently decreases with LEA and reflects energy status 6
  • IGF-1: May decrease with chronic LEA, though less consistently than leptin 6

Bone Health Assessment

Bone Turnover Markers

  • βCTX-1 (C-terminal telopeptide): Marker of bone resorption—increases with LEA 6
  • P1NP (procollagen type 1 N-terminal propeptide): Marker of bone formation—decreases with LEA 6
  • Rationale: Approximately half of LEA interventions show significant increases in bone resorption and decreases in bone formation within days

Bone Mineral Density

  • DXA scan (dual-energy X-ray absorptiometry) of lumbar spine and whole body (head excluded in adolescents) 1
  • When to order: For athletes with LEA indicators, amenorrhea >6 months, history of stress fractures, or disordered eating 1
  • Interpretation: Z-score <-1.0 warrants attention in athletes (who should have 5-15% higher BMD than non-athletes); <-2.0 with risk factors indicates osteoporosis 1

Nutritional Deficiency Screening

Essential Micronutrients

  • Vitamin D (25-hydroxyvitamin D): Target >90 nmol/L for athletes 7, 3
  • Iron studies: Ferritin, serum iron, total iron-binding capacity, hemoglobin 8
  • Complete blood count (CBC): To assess for anemia 1
  • Calcium: Part of calcium metabolism assessment 1

Common pitfall: Vitamin D deficiency is extremely prevalent in athletes and compromises immunity, muscle repair, and bone health—don't overlook this even when other markers appear normal 8, 3

Additional Considerations

Androgen Profile (When Indicated)

  • Order when evaluating for polycystic ovary syndrome or other causes of menstrual dysfunction 1

Body Composition

  • Fat-free mass measurement via DXA or other validated methods 5
  • Rationale: Needed to calculate energy availability (EA = [Energy Intake - Exercise Energy Expenditure] / Fat-Free Mass) and interpret BMD results

Practical Implementation Strategy

Step 1: Start with the core panel (reproductive hormones, thyroid function, CBC) when LEA is suspected based on clinical presentation (menstrual dysfunction, stress fractures, unexplained performance decline, weight loss)

Step 2: Add bone turnover markers and vitamin D for athletes with chronic symptoms or high-risk sports (endurance, aesthetic, weight-class sports) 7, 1

Step 3: Order DXA scan for any athlete with amenorrhea >6 months, recurrent stress fractures, or confirmed chronic LEA 1

Step 4: Reassess BMD every 12 months in adults or minimum 6 months in adolescents being treated for low BMD 1

Critical Caveats

  • Timing matters: For accurate LH and FSH characterization, overnight sampling at 3-6 hour intervals is ideal, though impractical in clinical practice 7. Single measurements are acceptable for screening but may miss pulsatile variations.

  • Weight stability is misleading: Athletes can be weight-stable yet have problematic LEA due to metabolic adaptation. Don't rely on stable weight to rule out LEA 5, 2

  • Hormonal contraception confounds results: Document use of hormonal contraceptives as they mask menstrual dysfunction and alter hormone levels 7

  • Reproductive function is more reliable than EA calculation: Current evidence suggests that reproductive hormone assessment provides more objective markers of optimal energy status than error-prone dietary intake and exercise expenditure calculations 4

  • Short-term vs. chronic LEA: Biomarker responses differ between acute experimental LEA (days) and chronic field-based LEA (months to years). Testosterone and bone markers show earlier changes than IGF-1 or inflammatory markers 6, 9

The 2023 IOC consensus emphasizes that problematic LEA represents maladaptive responses with persistent disruption of body systems, distinguishing it from adaptable short-term energy deficits 2. Laboratory testing helps identify which athletes have crossed from adaptable to problematic LEA, guiding intervention urgency.

References

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.